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David Letterman marks his 30th anniversary in late night TV comedy Wednesday, matching his hero, Johnny Carson, if only in terms of durability.

After three decades of trying to become the next Carson, the irascible and endlessly self-critical Letterman should allow himself a moment to savor a unique career with enough highlights to fill a slew of Top 10 lists.

Not that he's celebrating. Save for CBS promos mentioning Letterman's 30 years as post-prime time TV comedy force, the only apparent nod to what should be a big day is the booking of Howard Stern, a favorite guest whose role as a radio comedy groundbreaker has run on parallel tracks as Letterman's TV reign, in time and influence.

In the weekday late-night comedy continuum, there's Carson and then everybody else. But his most direct descendant, Letterman, arguably has exerted a greater influence on the current late-night landscape, one he helped expand far beyond "The Tonight Show." If Carson is the granddaddy of them all, then Letterman is the cranky, favorite uncle who is both inspiration and competition for his younger peers.

Letterman's "the guy who lives under the seats" is a forbearer of recurring characters like Conan O'Brien's bear with a self-gratification obsession. Letterman’s CBS Mailbag is a chain letter leading to Jimmy Fallon’s Audience Suggestion Box. Letterman’s penchant for sarcasm is channeled through the loose lips of Jimmy Kimmel and Chelsea Handler. The filmed reports and interviews on "The Daily Show" and "The Colbert Report" owe a debt to the days when Letterman regularly would venture outside 30 Rock and The Ed Sullivan Theater (remember his visit to Just Bulbs?). And musicians across late night TV should be grateful to Paul Shaffer for bringing talk show music into the post-Big Band era.

Over the years, Letterman, who famously feuded with the one-named stars like Oprah, Cher and Madonna, has become somewhat more tolerant of others, if not necessarily kinder. He still managed to infuriate Sarah Palin, though, with cracks about her family in 2009. Nearing 65, he’s not donning Velcro and Rice Krispies suits anymore, but still drops things off the roof and chucks footballs at the giant meatball atop his Christmas tree. The show no longer carries the dangerous air of unpredictability once fanned by Andy Kaufman's attack on Jerry Lawler, Crispin Glover's high kicks and Penn and Teller's roach stunt. But who could have guessed Letterman would have become the victim of an extortion attempt that revealed his own surprising sexual peccadilloes?

Unlike Carson, Letterman’s gotten through his 30-year stint without guest hosts, save for during his recovery from heart surgery in 2000, a life-changing experience that clearly made him more introspective. His finest moment came a little over a year and a half later, in his first show after the 9/11 attacks, in which he eloquently echoed the confusion, sadness and fury of a nation. "If you live to be a thousand years old, will that make any sense to you?” he asked. “Will that make any goddamned sense?"

Perhaps Letterman’s greatest entertainment accomplishment is becoming the first late night TV comedy host after Carson to establish an enduring career in the genre, paving the way for others, including the smart and quirky Craig Ferguson, who occupies the spot after “Late Show With David Letterman.” Letterman had the benefit of honing his own irreverent act for a decade in the slot after “The Tonight Show,” beginning with the first “Late Night with David Letterman” on NBC February 1, 1982.

Jay Leno, a formidable force himself, got the post Letterman desperately wanted after Carson stepped down nearly 20 years ago. Even after Letterman moved to the 11:30 p.m. spot for CBS in 1993, Leno bested him in the ratings – and generally continues to do so after getting his old job back from O'Brien nearly two years ago.

Letterman never wanted to be Leno. He'll never be Carson. Just being Dave, after all these years, is an impressive human trick that may never satisfy him, but is enough to keep us watching.